USB AM TO USB AF Apply in the switch over and Extension for all kinds of USB Devices.

USB bus interface handles the interconnceting between electrical layer and protocol layer. From the perspective of the interconnecting, The similiar bus interface is simultaneously given by the device and the host. For example, a serial interface engine (SIE), USB bus interface is implemented by the host controller. USB system uses host controller to manage the data transmission between host and USB devices. The interfaces between USB system and the host controller  is dependent on the hardware definitions of host controller. Meanwhile, USB system is also responsible for the management of USB resources, such as bandwidth and bus energy, which is possible to enable customers to access USB. There are three basic components in the USB System: The firs is the host controller driver (HCD) which can map different host controller device to the USB system. The second is called HCDI  which lies in between HCD between HCDI. Specific HCDI is defined by the operating systems of supporting different host controllers. The third is  universal host controller driver (UHCD) which lies at the bottom of soft structure and it has to manage and control the main controller. UHCD has achieved communicating with the USB host controller and controlling USB host controller. And it is hidden from other parts of system software. The most high-level of system software communicates by the software interface of UHCD and main controllers.